rr 

<3L  4v*£Z&- 

1 ' - v "h  CL*»  4~  r rrfUf  ; 

A COMPENDIOUS  VIEW 

OP  THE 

REMARKABLE  FACTS 


RECENT  DISCOVERIES 


ELECTRO-MAGNETISM 


MAGNETO -ELECTRICITY. 


BY  FREDERICK  A.  P.  BARNARD,  A.  M. 

I' 


NEW- YORK : 

GEORGE^EARBORN  AND  CO. 

* NO.  38  GOLD  STREET. 


Scatchcrd  and  Adams,  Printers. 

1837. 


B,us. 


{ 


T 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/compendiousviewoOObarn 

( 


ELECTRO-MAGNETISM 


What,  in  the  entire  range  of  nature  and  nature’s  works,  is  so 
wonderful  as  electricity  ? What,  rather,  in  the  circle  of  natural 
phenomena,  is  not,  in  one  way  or  other,  directly  or  indirectly,  con- 
nected with  this  mysterious,  all-pervading,  and  fearfully  energetic 
principle  1 Above,  around,  beneath — nay,  even  within  our  very 
selves — we  find  it  ever  present,  ever  active.  Whether  we  contem- 
plate its  sublimely  splendid  coruscations  blazing  along  the  heavens, 
or  its  more  quiet,  and  often  more  gorgeous  magnificence  as  it 
streams  upward  from  the  pole,  or  its  hidden  agency  in  quickening  to 
life,  and  clothing  with  beauty  the  whole  animal  and  vegetable 
world,  or  regulating,  in  the  deep  caverns  of  the  earth,  the  labora- 
tories of  nature — the  ceaseless  decompositions  and  recompositions 
of  matter ; whether  we  regard  it  in  its  power,  and  clothed  in  its 
robe  of  terrors,  speaking  in  thunders,  shivering  in  splinters  the 
stoutest  monarchs  of  the  forest,  and  prostrating  in  the  dust  the 
proudest  fabrics  of  human  art,  or  in  its  beauty  and  beneficence, 
breathing  vitality  into  all  the  myriad  forms  of  sentient  existence, 
and  scattering  around  them  sources  of  enjoyment  varied  to  infinity  ; 
in  whatever  light  we  view  this  wonderful  emanation  of  creative  power 
— the  handmaid  of  creation  itself — new  marvels  ceaselessly  dawn 
- upon  us,  and  our  imaginations  are  borne  away  in  loftier  and  loftier 
flights,  till  we  grow  even  giddy  with  our  elevation,  and  almost 
shudder  as  we  gaze  through  the  wide  expanse  it  has  revealed  to  us. 

Nor  is  it  among  the  least  of  our  wonders,  to  reflect  that  we  are 
even  yet  upon  the  threshold  of  discovery.  The  science  of  elec- 
tricity, stupendous  as  it  is,  is  but  an  infant  science  still.  A half 
century  has  not  yet  passed  away  since  the  first  detection  of  galvanic 
currents.  Never,  perhaps,  before  nor  since,  was  there  made  a dis- 
covery productive  to  science  of  consequences  so  vast,  so  splendid. 


2 


and  so  rapidly  succeeding  one  another,  as  those  which  have  flowed 
from  this.  First  in  order  came  electro-chemistry,  unlocking  all  the 
secrets  of  matter,  dissolving  nature’s  most  curious  compounds,  and 
reducing  all  things  to  their  original  elements — a science  which  has 
more  recently  unravelled  the  laws  of  the  composition,  as  well  as  of  the 
separation  of  elements,  and  revealed  to  us,  doubtless,  the  agent  first 
employed  by  creative  energy,  to  bring  order  and  beauty  out  of  the 
primeval  chaotic  ocean.  To  this  have  succeeded  electro-dyna- 
mics, electro-magnetism,  thermo-electricity,  magneto-electricity, 
and  (if  the  term  has  not  been  used  it  should  be)  electro-physiology 
— all  new  ramifications  of  a single  science,  growing  up  together, 
and  each  unfolding  to  us  its  own  peculiar  catalogue  of  wonders. 
Of  the  first  two  of  these,  and  of  magneto-electricity,  we  shall  have 
occasion  to  speak  at  large.  The  curious  discovery  by  Professor 
Seebeck,  of  the  generation  of  electricity  by  heat,  with  the  more  re- 
cent inquiries  of  Becquerel,  Nobili,  and  Melloni,  Cumming,  Faraday, 
and  Andrews,  renders  it  more  than  probable  that  we  shall  yet  be 
compelled  to  strike  caloric,  as  we  have  done  magnetism  already, 
from  the  list  of  distinct  imponderable  agents.  Light,  too,  if  the 
observations  of  Morichini  and  Mrs.  Somerville  should  be  confirmed, 
may  yet  be  forced  to  add  another  braneh  to  electrical  science, 
which  some  future  philosopher  may  denominate  Photo-Electricity. 
The  wonderful  discoveries  of  Becquerel,  in  animal  and  vegetable 
electricity,  are  possibly  about  to  throw  a flood  of  illumination  upon 
the  science  of  pathology,  and  the  healing  art,  as  well  as  upon  the 
culture  of  plants,  to  subserve  the  purposes,  or  to  gratify  the  taste  of 
man. 

Should  the  identity  of  light  and  heat  with  electricity  be  esta- 
blished, what  then  of  our  imponderable  agents  will  remain  ? Gravi- 
tation stands  alone — and  who  shall  say  that  even  this,  like  the  rest, 
will  not  be  ultimately  swallowed  up  by  electricity  ; leaving  but  a 
single  essence  in  the  universe,  too  ethereal  to  be  matter,  yet  too 
passive  and  too  inert,  if  not  too  gross,  to  be  spirit  ? To  this  opi- 
nion we  confess  ourselves  inclined.  Its  correctness  is  a question, 
which,  if  settled  at  all,  will  probably  be  settled  in  another  age. 

However  fertile  and  animating  a theme  for  speculation  and  de- 
clamation is  afforded  us  by  the  wonderful  discoveries  at  which  we 
have  just  been  glancing,  we  propose,  in  the  present  article,  to  re* 


3 


strict  ourselves  to  a series  of  simple  statements  of  fact.  The  sci- 
ence of  electro-magnetism — a science  of  not  yet  twenty  years* 
growth,  and  one  which  has  only  acquired  its  importance  within  less 
than  ten,  has  become,  in  consequence  of  its  practical  applications, 
a subject  of  general  interest  to  mankind.  Few  have  leisure  for  the 
perusal  of  scientific  treatises  ; and,  were  it  otherwise,  they  would 
seek  in  vain  for  one  which  would  exhibit  to  them  the  science  under 
consideration  in  its  present  state.  The  last  five  or  six  years  have 
added  a world  to  the  sum  of  preceding  discoveries ; and  the  sub- 
stance of  this  is  still  scattered  through  the  scientific  transactions 
and  journals.  There  are  very  many  persons,  nevertheless,  who 
would  be  gratified  even  with  such  a hasty  outline  of  the  subject,  as 
a few  pages  of  a magazine  devoted  to  literature  will  admit.  They 
wish  to  think  of  something  more  than  a name,  when  the  title  of 
this  much  talked  of,  but  little  understood,  science,  falls  upon  their 
ears.  To  such,  the  following  sketch  will,  without  doubt,  prove  ac- 
ceptable. 

The  first  indication  of  the  positive  relation  existing  between 
electricity  and  the  magnetic  power,  was  observed  in  1819,  by  Pro- 
fessor CErsted,  of  Copenhagen.  This  philosopher  ascertained  that 
an  electric  current,  passing  along  the  wire  used  to  connect  the  ex- 
tremities of  a galvanic  battery,  possesses  power  to  deflect  the  mag- 
netic needle  in  a remarkable  manner.  If  this  wire,  conveying  a 
positive  electric  current  from  north  to  south,  be  placed  horizontally 
over  the  needle,  and  therefore  parallel  to  it,  the  north  pole  of  the 
needle  is  turned  toward  the  east.  If  it  be  placed  in  like  manner 
below,  the  same  pole  is  carried  toward  the  west.  If  it  be  removed 
to  the  east  side,  the  pole  is  depressed  ; if  the  west,  it  is  elevated. 
The  effects  produced  by  a similar  current  on  a south  magnetic 
pole,  are  precisely  the  reverse.  Accordingly,  since  in  the  rotation 
of  a needle  suspended  by  its  centre,  the  two  ends  move  always  in 
opposite  directions,  both  forces  conspire  to  increase  the  effect  pro- 
duced upon  it  by  a single  electric  current. 

These  appearances,  at  first  view,  seem  to  be  singularly  anoma- 
lous. They  are  dependent,  nevertheless,  on  a simple  law,  which 
may  be  illustrated  by  the  following  artifice.  Suppose  that,  upon 
the  wire  placed  north  and  south  as  before,  a small  serrated  wheel  is 
made  to  revolve  constantly  in  the  direction  in  which  the  sun  passes 


4 


over — that  is,  from  east  to  west ; the  lower  part  of  this  wheel 
will,  of  course,  return  from  west  to  east.  If  we  bring  down  the 
wire  from  above  to  the  needle,  so  that  the  teeth  of  the  wheel  may 
strike  the  north  pole,  that  pole  will  be  carried  along  with  them  to 
the  east.  But  if  the  wire  be  brought  upward  from  below,  then  the 
teeth  of  the  wheel,  moving  in  the  direction  of  the  sun,  will  carry 
the  pole  toward  the  west.  As  the  teeth  descend  on  the  left,  and 
ascend  on  the  right,  (we  suppose  ourselves  facing  the  north,)  the 
elevation  or  depression  of  the  pole,  according  as  the  wire  is  on  the 
west  or  the  east  side  of  the  needle,  admit  of  explanation  with  equal 
facility.  The  phenomena  are,  therefore,  precisely  such  as  would 
be  produced  by  a rotary  or  circular  force,  referred  to  the  wire  as 
an  axis.  As  the  magnetic  pole,  acted  on  by  this  force,  is  moved 
in  a tangent  to  the  circle,  the  force  has  itself  been  called  tangential . 

Professor  CErsted’s  discovery  at  once  aroused  the  curiosity,  and 
stimulated  to  activity  the  ingenuity,  of  the  whole  philosophic  world. 
M.  Arago  and  Sir  Humphrey  Davy  soon  discovered  that  the  con. 
necting  wire  of  the  battery,  beside  exerting  this  singular  and  ap- 
parently repulsive  power  upon  a magnetic  pole,  exhibited  also,  dur- 
ing the  passage  of  the  current,  the  ordinary  magnetic  attraction 
upon  unmagnetized  iron  and  steel,  in  a high  degree.  Thus,  it  would 
sustain  a mass  of  iron-filings  of  a dozen  times  its  own  diameter  : 
but  these  instantly  fell  away,  on  the  cessation  of  the  current.  The 
philosopher  last  mentioned  found,  moreover,  that  steel  needles, 
placed  near  the  current  transversely,  or  at  right  angles  to  its  course, 
became  instantaneously  and  permanently  magnetic  ; while  other 
needles,  placed  parallel  to  the  current,  exhibited  the  same  magnetic 
properties  as  the  conducting  wire,  but  lost  them,  in  like  manner, 
when  the  current  ceased.  The  induction  of  magnetism  by  elec- 
tricity was  thus  early  demonstrated.  In  its  practical  consequences, 
this  discovery  bids  fair  to  rank  among  the  first  in  importance, 
ever  made  in  philosophy. 

From  a consideration  of  the  law  of  tangential  force  explained 
above,  it  seemed  obvious  that  a magnetic  pole,  free  to  move  in  any 
direction,  and  prevented,  at  the  same  time,  from  so  far  obeying  the 
centrifugal  force  as  to  be  thrown  beyond  the  influence  of  the  elec- 
tric current,  ought  to  revolve  in  a circle  about  the  conducting  wire. 
This  inference,  first  drawn  by  Dr.  Wollaston,  was  practically  con- 


6 


firmed  by  Mr.  Faraday,  with  the  aid  of  a very  simple  apparatus. 
One  end  of  a bar  magnet  was  attached  by  a thread  to  the  bottom 
of  a vessel  of  mercury,  in  which  the  magnet  floated  almost  upright. 
An  electrical  current  was  then  introduced  into  the  centre  of  the 
mercury,  by  means  of  a terminated  wire,  and  carried  off  below  by 
another  wire,  passing  through  the  bottom  of  the  vessel.  The  mag- 
net instantly  began  to  revolve,  and  continued  its  motion  while  the 
current  lasted.  Action  and  re-action  in  mechanics  being  equal,  it 
followed,  of  course,  that  the  conducting  wire  might  be  made  to  re- 
volve about  a magnet.  This  effect  was  produced  by  an  arrangement 
nearly  similar  to  the  former,  the  magnet  being  fixed,  and  the  wire 
provided  with  a joint.  By  rendering  both  the  magnet  and  the  wire 
moveable  in  the  same  apparatus,  both  phenomena  were  exhibited 
at  once.  Fluid  conductors,  like  mercury  and  water,  contained  be- 
tween concentric  glass  cylinders,  were  also  made  to  revolve  about  a 
magnetic  pole.  Magnets  and  conductors  were  made  to  revolve 
on  their  own  axes  ; and,  finally,  the  galvanic  battery  employed  to 
generate  the  electric  current,  having  been  constructed  very  light 
and  suspended  with  delicacy,  was  itself  forced  to  make  the  circuit. 
This  battery  being  composed  of  hollow  cylinders  with  the  magnet 
in  the  centre,  it  was  even  found  possible  to  produce,  at  the  same 
time,  independent  rotations  of  the  zinc  and  copper  plates,  in  con- 
trary directions.  It  must  be  observed  of  all  these  rotations,  that 
their  directions  were  reversed,  by  reversing  that  in  which  the  elec- 
tric current  passed. 

These  phenomena  are  all  curious  and  interesting.  They  demon- 
strate a relation  to  exist  between  the  principles  of  magnetism  and 
electricity ; but  they  afford  little  evidence  of  similarity — much  less 
of  absolute  identity — between  them.  It  is  otherwise  with  those  we 
are  about  to  describe. 

Let  a piece  of  copper  wire  be  bent  into  a circle  of  about  an  inch 
in  diameter,  the  extremities  not  being  allowed  to  meet,  but  being 
again  bent  so  as  to  pass  off  a little  distance  in  parallel  lines,  and 
terminate  in  hooks.  Through  the  wire  suspended  by  these  hooks 
in  the  manner  usually  practised  by  experimenters  in  Volta-electri- 
city,  let  an  electric  current  be  transmitted.  The  pole  of  a magnet 
being  then  presented  to  the  centre  of  the  circle,  an  attraction  will 
be  manifested  on  one  side  and  a repulsion  on  the  other.  That  is, 


6 


the  circle  will  approach  the  magnet  so  as  to  surround  it,  in  the  first 
instance  ; and  will  recede  from  it,  in  the  second.  If  the  other  pole 
of  the  magnet  be  presented,  the  effects  will  be  severally  reversed. 
An  explanation  of  this  phenomenon  may  easily  be  found  in  the  law 
of  tangential  force.  For,  if  we  suppose  this  force  to  be  visibly  re- 
presented by  a number  of  toothed  wheels  revolving  round  the  wire’ 
we  shall  perceive  that  their  effect  on  one  side  will  be,  to  draw  the 
magnet  into  the  circle ; and,  on  the  other,  to  drive  it  out. 

These  phenomena  of  attraction  and  repulsion,  correspond  exactly 
with  those  of  magnetic  polarity.  And,  indeed,  the  circle  may  be 
considered  to  represent  a magnet,  having  considerable  breadth  and 
an  exceedingly  short  axis. 

Various  devices  have  been  contrived  to  render  the  resemblance 

» 

thus  discovered,  to  a common  magnet,  more  striking.  M.  A.  De 
La  Rive  attached  a circle  like  that  just  described,  to  narrow  slips 
of  zinc  and  copper,  passing  through  a cork  of  sufficient  buoyancy 
to  float  the  whole  in  an  acid  or  saline  bath.  These  slips  of  metal 
thus  immersed,  constituted  the  battery  : while  the  lightness  of  the 
apparatus  and  its  perfect  freedom  of  motion,  well  adapted  it  to  the 
purpose  intended.  The  power  of  this  little  apparatus  was  increased, 
by  causing  the  wire  to  make  several  complete  circles,  before  at- 
taching it  to  the  battery  ; the  wire  having  been  itself  first  insulated 
by  winding  with  silk,  in  order  to  force  the  electricity  to  traverse 
its  entire  length. 

A still  nearer  approach  to  the  magnet  is  made,  by  separating  to 
a little  distance  from  each  other  laterally,  the  coils  of  wire  in  this 
improved  apparatus  of  Mr.  De  La  Rive,  so  as  to  produce  a spiral 
cylinder,  or  helix . The  number  of  turns  may  be  increased  at  plea- 
sure. The  ends  of  the  coiled  wire  are  carried  back  along  the  axis 
of  the  helix,  till  they  meet  half-way  ; and  afterward  at  right  angles 
downward  to  the  floating  battery.  This  elongation  of  the  coil  se- 
parates the  poles,  one  being  found  at  each  end  of  the  helix.  The 
whole,  if  constructed  with  delicacy,  will  obey  the  magnetic  influence 
of  the  earth,  and  settle  itself  with  the  axis  of  the  helix  in  the  mag- 
netic meridian. 

When  this  position  has  been  spontaneously  assumed,  positive 
electricity,  if  the  helix  be  wound  like  the  thread  of  a screw,  will  be 
moving  from  south  to  north  ; and,  consequently,  in  the  upper  half  of 


7 


each  coil  of  the  spiral,  from  west  to  east : but,  in  a helix  wound  in 
the  opposite  direction,  the  current  will  be  from  north  to  south  ; that 
is,  in  the  several  coils  of  the  spiral,  from  west  to  east  still.  If,  then, 
instead  of  the  helix,  we  had  but  a single  circle  of  wire,  in  the  cir- 
cuit, theory  would  require  that  this  should  assume  a position,  under 
the  influence  of  terrestrial  magnetism,  at  right  angles  to  the  mag- 
netic meridian.  Experiment  with  a circle  of  some  size,  delicately 
suspended,  confirms  this  inference.  And  not  only  that,  but,  with 
suitable  arrangements,  a similar  circle  will  be  brought  by  the  pow- 
er of  the  earth’s  magnetism,  to  stand  with  its  plane  precisely  at 
right  angles  to  the  line  of  the  dip. 

Helices  constructed  as  above  described,  exhibit  all  the  phenomena 
of  ordinary  magnetism.  Their  similar  poles  repel  each  other,  and 
repel  those  of  steel  magnets ; and  their  dissimilar  poles  exert  reci- 
procal attraction,  and  attract  the  dissimilar  poles  of  magnets.  We 
should  be  warranted,  even  here,  in  concluding  the  phenomena  of 
ordinary  magnetism  to  be  simple  manifestations  of  electric  energy. 
On  this  supposition,  the  common  magnet  must  be  encircled  by  cur- 
rents of  electricity  moving  at  right  angles  to  its  axis ; and  the 
earth  itself  must  be  traversed  by  similar  currents,  passing  round  it 
from  east  to  west.  That  the  effect  of  such  currents  upon  the  mag- 
netic needle,  would  be  precisely  such  as  we  see  to  be  actually  produc- 
ed by  the  influence  of  terrestrial  magnetism,  was  experimentally  de- 
monstrated by  Mr.  Barlow,  in  1831,  by  means  of  an  artificial  globe. 
We  may  add,  furthermore,  that  experiments  made  by  Mr.  Robert 
Were  Fox  in  the  mines  of  Cornwall,  seem  to  prove  the  actual  ex- 
istence of  such  currents  in  the  earth. 

The  power  of  magnetic  induction,  that  is,  of  exciting  magnetism 
in  unmagnetized  bodies,  has  already  been  mentioned  as  remarkably 
belonging  to  electricity  moving  in  currents.  This  power  is  won- 
derfully increased  by  causing  the  current  to  pass  through  a heliacal 
conductor,  and  placing  the  bar  to  be  magnetized  within  the  coil. 
Hardly  an  instant  is  necessary  to  produce  the  effect.  In  soft  iron, 
the  magnetism,  as  when  excited  by  the  common  methods,  is  but 
temporary  : in  steel,  it  is  permanent. 

The  power  developed  by  winding  large  bars  of  soft  iron  with 
copper  wire  covered  with  silk  or  cotton,  is  in  the  highest  degree 
astonishing.  In  1829  or  30,  Professor  Moll  of  Utrecht  produced  a 


8 


horse-shoe  magnet  of  this  description,  capable  of  sustaining  more 
than  one  hundred  and  fifty  pounds.  But  Professor  Henry  and  Dr. 
Ten  Eyck  of  our  own  country,  who  were  carrying  on  a simultaneous 
and  independent  series  of  experiments,  accomplished  wonders  im- 
mensely greater.  Their  most  powerful  magnets  sustained  about  a 
ton. 

In  the  construction  of  magnets  of  this  description,  it  is  found  that 
the  power  acquired  is  not  in  exact  proportion  to  the  number  of  coils 
made  by  the  surrounding  wire.  Were  it  so,  nothing  could  impede 
the  attainment  of  any  proposed  power,  even  with  a battery  of  mode- 
rate size,  by  the  mere  multiplication  of  the  number  of  coils.  The 
current  appears  to  become  enfeebled  in  traversing  a long  circuit. 
Thus,  Professor  Henry  found  that,  after  having  wound  his  great 
magnet  in  such  a manner  that  he  could,  at  pleasure,  either  send  the 
electricity  in  a single  current  through  the  whole  length  of  the  en- 
circling wire,  or  in  divided  portions,  passing  each  through  a part  of 
the  wire  disconnected  from  the  rest,  the  power  of  the  magnet  was 
immensely  greater  in  the  latter  case  than  in  the  former,  though  the 
battery  remained  unchanged. 

From  a consideration  of  such  phenomena,  it  appeared  probable 
to  Professor  Emmet  of  Virginia,  that  the  power  of  an  electro-mag- 
net  could  not  be  dependent  on  the  number  of  circuits  made  by  the 
electric  fluid  around  the  bar,  but  rather  upon  the  collected  volume 
of  the  whole.  By  inference,  therefore,  there  is  no  necessity  for 
using  wire  in  the  construction  of  these  magnets  ; but,  in  its  stead, 
we  may  employ  metallic  sheets  in  which  to  roll  the  iron  to  be  mag- 
netized— these  sheets  being,  of  course,  insulated  from  the  iron  and 
from  their  own  convolutions,  by  interposed  silk.  His  experiments 
seemed  to  corroborate  the  truth  of  his  supposition,  very  powerful 
electro-magnets  having  been  constructed  by  him,  by  the  use  of  sheet 
copper. 

The  length  of  the  magnetized  bar  seems  to  have  much  to  do  with 
the  power  attained.  From  some  experiments  detailed  to  the  Royal 
Society  in  1833,  by  Dr.  Ritchie,  it  would  appear  that  short  bars, 
with  a given  quantity  of  enveloping  wire,  have  much  the  advantage. 
Of  two  horse-shoe  magnets,  having  lengths  as  one  to  four,  wound 
with  the  same  quantity  of  wire  each,  and  magnetized  by  the  same 
battery,  the  result  was  in  favor  of  the  short  one  in  the  ratio  of  two 


9 


to  one.  Having  afterward,  as  he  says,  prepared  a horse-shoe  mag- 
net  with  great  pains,  according  to  the  American  method,  and  found 
its  power  to  be  about  one  hundred  and  forty  pounds,  he  simply 
rolled  twelve  feet  of  copper  ribbon  about  the  lifter,  (the  piece  of 
iron  laid  across  the  poles  of  a horse-shoe  magnet)  and,  employing 
that  as  the  magnet,  made  the  horse-shoe  itself  serve  as  a lifter  in 
turn.  The  lifter  proved  the  more  powerful  magnet  of  the  two. 
“ All  that  is  necessary,  then,’’  he  says,  “ to  make  a powerful  electro- 
magnet, is  simply  to  roll  a ribbon  of  copper  about  a short  bar  of 
iron,  and  use  a horse-shoe  lifter.” 

Wonderful  as  the  immense  power  thus  instantaneously  called  into 
action,  by  means  the  most  simple,  appears  to  us,  our  astonishment 
becomes  still  greater,  when  we  consider,  not  only  that  it  may  just  as 
instantaneously  be  reduced  to  nothing,  but,  that  what  was  just  now 
attraction,  may  be  converted,  in  the  twinkling  of  an  eye,  into  the 
most  powerful  repulsion.  This  arises  from  the  fact  that  the  direc- 
tion of  the  induced  magnetic  poles  depends  on  that  of  the  electric 
current.  This  current  may  be  reversed  in  a space  of  time  too  mi- 
nute even  for  conception,  and  the  poles  are  reversed  along  with  it. 
In  late  years,  more  than  one  experimenter  has  essayed  to  turn  this 
principle  to  account  for  the  generation  of  motion.  Professor  Henry, 
of  this  country,  succeeded,  so  early  as  the  year  18.31,  in  producing  a 
reciprocating  motion  in  a horizontal  electro-magnetic  bar.  Early 
in  1833,  Dr.  Ritchie,  of  London,  obtained  a rapid  rotation  of  a si- 
milar bar,  at  first  under  the  influence  of  a horse-shoe  magnet  wide 
between  the  poles,  and  afterward  by  the  power  of  terrestrial  mag- 
netism alone.  The  account  of  this  invention  was  read  to  the  Royal 
Society  on  the  21st  of  March,  1833,  and  published  in  their  Trans- 
actions for  that  year.  From  the  paper  referred  to,  we  extract  the 
following  : — 

“ But  the  most  beautiful  result  I have  obtained  from  changing  the 
poles  of  an  electro-magnet,  is  the  rapid  rotation  of  such  a magnet 
about  its  centre.  The  following  short  description  of  the  first  actu- 
ally constructed,  will  be  sufficient  to  show  how  others  of  greater 
power  may  easily  be  formed.” 

[The  description  being  connected  with  a diagram,  we  alter  its 
phraseology  so  far  as  is  necessary  to  render  it  independently  in- 
telligible.] 


2 


10 


“ A circular  sole  of  wood  is  taken,  having  a groove  turned  in  it 
for  the  purpose  of  holding  mercury.  The  groove  is  divided  into  two 
compartments  by  thin  slips  of  wood.  These  divisions  are  to  be 
connected  with  the  poles  of  a battery.  An  electro-magnet  is  form- 
ed by  a piece  of  soft  iron  wound  with  copper  wire,  and  so  balanced 
on  its  centre,  that  the  ends  of  the  wire  shall  touch  the  mercury  in 
the  two  divisions  of  the  groove.  These  ends  are  so  adjusted  as  to 
clear  the  two  small  divisions  of  wood,  the  surface  of  the  mercury 
rising  a little  above  the  divisions.  If  a horse-shoe  magnet  having  a 
considerable  distance  between  the  poles,  be  "placed  above  the  tempo- 
rary magnet,  the  poles  of  the  permanent  magnet  being  directly 
above  the  slips  of  wood  which  divide  the  groove  into  two  compart- 
ments, whilst  the  soft  iron  is  converted  into  a magnet  by  means  of 
the  battery,  a powerful  and  rapid  rotation  of  the  electro-magnet  will 
take  place ; for  the  electro-magnet  being  put  in  motion  by  the  at- 
traction of  the  poles  of  the  other,  will  have  its  poles  reversed  the 
moment  the  wires  pass  the  two  divisions.  At  that  moment  attrac- 
tion will  be  changed  into  repulsion,  &c.  * * * 

“By  a slight  modification  of  the  apparatus,  horse-shoe  magnets 
may  be  made  to  revolve  with  considerable  force.  I have  fitted  up  a 
revolving  apparatus  of  this  kind,  which  has  a power  sufficient  to 
raise  several  ounces  over  a pulley.  When  the  apparatus  is  placed 
so  that  the  change  of  poles  of  the  electro-magnet  may  take  place 
in  the  magnetic  meridian,  the  action  of  the  earth  is  sufficient  to 
make  the  magnet  revolve,  without  the  aid  of  exterior  magnets.  By 
fitting  it  up  so  as  to  revolve  in  the  plane  of  the  magnetic  meridian, 
and  to  change  its  poles  at  the  point  to  which  the  needle  dips,  a dip- 
ping needle  might  be  made  to  revolve  in  a vertical  plane.” 

In  July,  1834,  our  countryman,  Mr.  Davenport,  with  no  know- 
ledge of  Dr.  Ritchie’s  previous  success,  obtained  a rotary  motion 
upon  identically  the  same  principle.  Since  that  time  he  has  de- 
voted himself  perseveringly  to  the  perfection  of  his  machine,  till  at 
length  his  triumphant  results  seem  about  to  produce  an  entire  revo- 
lution in  mechanics.  As  Americans,  we  are  proud  of  the  man,  who, 
under  the  weight  of  a thousand  disheartening  embarrassments,  has 
at  last  demonstrated  to  the  world  the  practicability  of  employing 
the  tremendous  energy  of  electro-magnetism,  as  a moving  power. 
Mr.  Davenport  has  associated  his  name  imperishably  with  the  his- 
tory of  the  science  he  has  espoused,  and  with  the  progress  of  im- 
provement in  the  entire  range  of  the  arts  ; to  which  his  labors  will 
be  found  hereafter  to  have  contributed  in  a thousand  ways.  To  him 
also  is  no  doubt  due  all  the  credit  of  having  independently  devised 
the  mode  of  producing  rotary  motion,  on  which,  as  recently  pub- 
lished, the  history  of  his  machine  informs  us,  his  patent  rests. 

But  let  us  not  on  this  account  indulge  ourselves  too  freely  in  ex* 


11 


elusive  laudation  of  American  ingenuity,  nor  decry  in  too  wholesale 
terms  the  importance  of  attending  to  the  past  labors  of  scientific 
men.  After  all,  as  a Persian  would  say,  the  philosophers  are  some- 
body. We  are  quite  too  apt  in  this  country  to  make  ourselves  ri- 
diculous in  the  eyes  of  foreigners,  by  our  extravagant  and  some- 
times ignorant  self-complacency.  Mr.  Davenport  was,  no  doubt,  an 
original  discoverer,  but  he  was  not  the  first  discoverer  of  the  princi- 
ple of  his  machine.  We  have  for  some  months  been  looking  for  the 
circumstantial  statement  of  this  fact  in  the  English  journals.  In 
the  mean  time,  we  have  seen,  in  our  own,  commendations  lavished 
upon  our  ingenious  fellow-citizen,  strictly  for  his  inattention  to  the 
writings  of  the  great  discoverers  in  this  department  of  science ; on 
the  ground,  forsooth,  that,  by  reading,  he  might  have  bound  down 
his  genius  for  ever  to  the  less  aspiring  notions  of  the  philosophers,  or 
have  been  led  away  wandering,  in  the  hopeless  mazes  in  which  they 
had  lost  themselves.  Had  Mr.  Davenport  read,  however,  he  would 
have  found  that  the  rotary  motion  he  was  seeking  for,  had  been  pro- 
duced, in  precisely  the  manner  in  which  he  has  since  produced  it, 
even  before  the  period  when,  as  we  are  informed,  he  “ saw  a galva- 
nic magnet  for  the  first  time.”  We  have  no  wish  to  detract  from 
the  credit  justly  due  to  perseverance  and  successful  ingenuity.  But, 
first  or  last,  Dr.  Ritchie  will  claim  the  priority  of  this  discovery,  and 
the  world  will  admit  the  justice  of  his  claim.  Mr.  Davenport  him- 
self, we  are  confident,  on  a comparison  of  dates,  would  not  hesitate 
to  do  the  same. 

Beside  the  attempts  already  noticed,  to  turn  the  power  of  electro- 
magnetism to  practical  account,  there  have  been  one  or  two  others 
deserving  of  a passing  mention.  Mr.  Sturgeon,  of  Woolwich,  con- 
structed a machine  of  considerable  power,  by  means  of  two  magnetic 
steel  bars  revolving  horizontally,  surrounded  by  four  fixed  upright 
electro-magnets.  Mr.  McGauly,  of  Ireland,  a year  or  two  since, 
reported  an  electro-magnetic  machine  to  the  British  Association ; 
but  the  volume  of  reports  containing  his  statements  is  not  at  hand 
at  present,  and  we  can  give  no  account  of  the  form  of  his  machine. 

We  have  heard,  moreover,  of  one  or  two  recent  inventions  in 
this  country,  but  are  not  aware  that  they  rest  on  any  new  prin- 
ciple. 

In  the  preceding  pages,  we  have  given  a cursory  outline  of  the 


12 


most  important  facts  in  the  science  of  electro-magnetism.  This 
term,  electro-magnetism,  so  long  as  the  phenomena  of  magnetism 
and  electricity  were  supposed  to  be  dependent  on  distinct  invisible 
agents,  possessed  a significancy,  which  it  has  now  in  a measure  lost. 
Magnetism,  which,  for  such  a length  of  time,  has  occupied  an  inde- 
pendent rank  among  the  physical  sciences,  is,  by  common  consent, 
transferred  to  a subordinate  place  in  the  more  comprehensive  sci- 
ence of  electricity ; and  its  phenomena,  with  those  of  the  particu- 
lar branch  we  are  considering,  are  to  be  referred  to  the  laws  of  that 
division  of  the  general  subject,  denominated  Electro-Dynamics . 

This  term  is  opposed  to  Electro-Statics ; the  one  science  treating 
of  electricity  in  motion  through  conductors,  and  the  reciprocal  action 
of  its  currents ; and  the  other,  of  common  electricity,  called  by 
Faraday  electricity  of  tension,  or  electricity  in  equilibrio.  The 
phenomena  characteristic  of  these  two  states  are  widely  different, 
as  will  be  evident  from  the  consideration,  that  two  bodies  charged 
with  similar  electricity  of  tension  repel  each  other,  and  with  dis- 
similar electricity,  attract ; while,  on  the  other  hand,  two  con- 
ductors carrying  similar  currents  in  the  same  direction,  attract,  and 
carrying  dissimilar,  repel.  This  last-mentioned  fact  is  at  the  basis 
of  the  science  of  electro-dynamics.  It  was  a discovery  of  Am- 
pere, a celebrated  French  philosopher,  made  soon  after  the  publica- 
tion of  (Ersted’s  experiments.  For  our  present  purpose,  it  will  be 
sufficient  to  show  in  what  manner  this  simple  law  may  serve,  instead 
of  the  supposition  of  a tangential  force,  to  explain  the  phenomena 
of  electro-magnetism.  Let  us  suppose  two  small  floating  batteries, 
like  the  apparatus  of  De  La  Rive  already  described,  to  be  brought 
near  to  each  other,  with  the  zinc  ends  in  the  same  direction.  It  is 
not  to  be  supposed  that  an  apparatus  of  so  little  power  and  so  great 
comparative  inertia,  would  actually  manifest  the  phenomena  we  are 
about  to  infer ; but  its  construction  is  favorable  to  the  illustration 
of  the  theory.  In  the  situation  described,  similar  electrical  cur- 
rents will  be  passing  in  the  same  direction  in  both  the  parallel 
circles,  and  the  two  should  accordingly  approach  each  other.  Let 
one  be  turned  half  a revolution  ; then,  as  the  currents  will  be  mov- 
ing in  contrary  directions,  separation  ought  to  take  place.  If  each 
circle  be  extended  as  above  described,  into  a helix,  (an  electro- 
dynamic cylinder,  in  the  language  of  M.  Ampere)  their  extremities 


13 


will  severally  manifest  contrary  polarities,  attracting  and  repelling 
one  another,  according  as  the  cylinders  are  so  arranged  that  the  cur- 
rents move  similarly  in  both,  or  the  contrary. 

From  this  rude  method  of  illustration,  we  are  not,  it  is  true,  at 
liberty  to  conclude,  at  once,  that  these  cylinders  will  manifest  all  the 
phenomena  of  ordinary  magnetism ; nor  even  that  they  will  con- 
tinue to  attract  and  repel  each  other  in  all  positions,  precisely  as 
magnets  would  do.  But  it  would  here  be  out  of  place  to  adduce  the 
mathematical  reasoning  by  which  all  the  observed  magnetic  pheno- 
mena are  legitimately  derived  from  the  one  fundamental  law  of 
electro-dynamics.  As  general  rules,  we  may  say  that  the  effect, 
according  to  this  law,  of  the  mutual  action  of  electric  cross  cur- 
rents, is  to  create  a tendency  to  parallelism  ; and  that,  when  cur- 
rents inclined  to  each  other,  are  both  approaching  toward,  or  both 
receding  from,  the  angle  of  their  inclination,  they  exert  a reciprocal 
attraction  ; but,  when  otherwise,  repel. 

The  application  of  these  principles,  and  of  some  others  which  it 
is  unnecessary  to  state,  is  sufficient  to  account  for  the  attraction 
and  repulsion  of  electro-dynamic  cylinders,  and  for  rotations  per- 
formed by  them,  and  by  conductors  in  their  vicinity,  like  those 
produced  by  the  use  of  magnets  ; as  well  as  for  additional  pheno- 
mena somewhat  similar.  But  all  this  will  not  enable  us  to  explain 
the  phenomena  of  electro-magnetism  without  supposing  the  exist- 
ence of  a tangential  force,  unless,  with  M.  Ampere,  we  regard  the 
common  magnet  as  an  electro-dynamic  instrument. 

Indeed,  in  view  of  all  the  wonderful  developements  of  modern 
science,  we  can  hardly  escape  from  the  conclusion,  that  the  polarity 
of  the  needle  is  owing  to  the  circulation  of  electric  currents  in  its 
substance.  M.  Ampere  supposes  each  particle  of  a magnetic  bar 
to  be  encircled  by  such  a current.  All  these  currents  moving  in 
the  same  direction,  (that  is,  from  west  to  east  on  the  upper  surface, 
when  the  bar  assumes  the  position  to  which  it  is  impelled  by  the 
action  of  terrestrial  magnetism)  those  in  the  interior  will  counteract 
one  another’s  effects  ; precisely  as  the  two  wheels  on  the  same  side 
of  a carriage,  would,  if  in  immediate  contact,  obstruct  each  other’s 
motion.  There  is  nothing,  however,  to  oppose  the  exterior  cur- 
rents, and  these  must  exert  an  influence  on  bodies  around  them, 
equivalent  to  that  of  a single  current  encircling  the  entire  magnet. 


14 


This  is,  in  few  words,  M.  Ampere’s  electro-dynamic  theory  of  mag- 
netism. Not  only  has  it  the  merit  of  simplifying  a hitherto  myste- 
rious class  of  phenomena,  but  it  explains,  much  more  satisfactorily, 
many  of  the  remarkable  rotations  we  have  described,  than  the  sup- 
position of  the  singular  force  denominated  tangential,  could  possibly 
do  ; to  say  nothing  of  the  contradiction  to  all  the  analogies  of  na- 
ture, implied  in  the  supposition  of  a force  so  altogether  unique. 

But  notwithstanding  the  general  disposition  to  admit  Ampere’s 
solution  of  the  mystery  of  magnetism,  it  was  felt  that  the  production 
of  some  phenomenon  decidedly  electric,  by  the  agency  of  magnetism 
alone,  would  be  an  important  corroboration  of  the  theory.  To  Mr. 
Faraday  must  be  ascribed  the  honor  due  to  the  accomplishment  of 
an  object  so  desirable,  and  the  developement  of  a new  series  of  won- 
ders in  the  world  of  science.  Toward  the  close  of  the  year  1831, 
after  a very  laborious  series  of  experiments,  that  philosopher  suc- 
ceeded in  producing  momentary  electrical  effects  from  a common 
magnet.  He  found  that  when  a helix  of  copper  wire  is  brought 
near  the  poles  of  a powerful  magnet,  electrical  currents  are  excited 
in  it.  These  are  increased  by  the  presence  of  a bar  of  soft  iron 
within  the  helix.  Similar  currents  are  generated  by  the  introduc- 
tion of  a bar  already  magnetised,  within  the  helix,  or  by  removing 
it  after  it  has  been  so  introduced.  These  are  observed  to  continue 
only  during  the  motion  of  the  bar  or  helix  ; and  cease  with  the  ces- 
sation of  the  motion,  though  the  parts  of  the  apparatus  maintain 
their  relative  situations.  The  first  indication  of  their  existence 
was  afforded  by  the  galvanometer ; but  they  became  subsequently 
much  more  obvious,  producing  convulsions  in  the  limbs  of  a frog, 
and  magnetising  steel  needles. 

With  the  new  light  thus  afforded  him,  Mr.  Faraday  next  directed 
his  attention  to  a class  of  phenomena  previously  altogether  inexpli- 
cable. M.  Arago  had  observed  something  very  like  magnetic  at- 
traction to  take  place  between  disks  of  various  substances  in  rapid 
rotation,  and  magnets  in  their  vicinity.  Sir  John  Herschell  and 
Mr.  Babbage  had  attributed  this  to  a temporary  magnetism  induced 
in  the  disks  by  the  magnet.  But  it  was  remarkable,  that,  with  the 
cessation  of  the  motion,  the  magnetism,  if  it  had  existed,  was  wholly 
lost.  Mr.  Faraday  did  not  hesitate  to  ascribe  it  to  electrical  cur- 
rents produced  by  magnetism  ; since  his  previous  experiments  had 


15 


proved  motion  to  be  essential  to  their  developement.  To  determine 
the  correctness  of  his  supposition,  he  caused  a disk  of  copper  to  re- 
volve,  with  its  edge  between  the  poles  of  a horse-shoe  magnet. 
Conductors  of  electricity  having  been  applied  to  the  centre  and  cir- 
cumference of  the  disk,  and  connected  with  a galvanometer,  his  con- 
jecture was  completely  corroborated. 

Mr.  Faraday  soon  demonstrated  that  the  circular  form  of  the 
moving  body  was  by  no  means  an  essential  condition.  Even  a sin- 
gle wire,  moved  in  the  vicinity  of  a magnetic  pole,  was  sufficient  to 
deflect  the  needle  of  the  galvanometer.  He  ascertained  the  general 
fact,  that  any  conductor  of  electricity  so  moved  as  to  cut  the  mag- 
netic curves,  (curves  into  which  iron  filings  are  observed  to  arrange 
themselves,  under  the  influence  of  a magnet)  was  invariably  tra- 
versed by  electrical  currents  at  right  angles  to  the  line  of  its  own 
motion. 

Proceeding  in  the  career  of  discovery,  he  found  that  terrestrial 
magnetism  alone  was  sufficient  to  excite  similar  currents.  “ It  is  a 
consequence,”  says  he,  “ which  appears  very  extraordinary  to  the 
mind,  that  scarcely  any  piece  of  metal  can  be  moved  in  contact 
with  others,  either  at  rest,  or  in  motion  with  different  velocities,  or 
in  other  directions,  without  currents  of  electricity  existing  within 
them.”  Mr.  Faraday  further  ascertained,  that,  when  a body  itself 
magnetic  is  made  to  rotate,  electrical  currents  are  excited  on  its 
own  surface  ; and  that  these  are  independent  of  the  currents,  which, 
4 according  to  M.  Ampere’s  theory,  give  it  polarity. 

A copper  disk  rotating  in  any  direction,  in  which  its  plane  did 
not  pass  through  the  line  of  the  dip,  was  found  to  constitute  an  elec- 
* trical  machine,  capable  of  sustaining  a constant  current,  passing 

through  conductors  connecting  its  centre  and  circumference.  The 
effect  was  greatest  at  right  angles  to  the  dip.  Currents  occurred  in 
a brass  globe,  in  whatever  direction  rotated.  The  axis  of  the  globe 
being  made  parallel  to  the  dipping  needle,  and  the  revolution  caused 
to  take  place  from  west  to  east,  the  effects  of  the  earth’s  diurnal 
motion,  in  producing  electrical  currents  within  itself,  were  exem- 
plified. These  currents  were  found  to  proceed  from  the  equator  to- 
ward both  poles.  There  is  not  a little  plausibility  in  the  theory 
respecting  the  Aurora  Borealis,  which  he  thus  modestly  sug- 
gests : — 


16 


“ I hardly  dare,  even  in  the  most  hypothetical  form,  to  ask  whe- 
ther the  Aurora  Borealis  and  Australis  may  not  be  the  discharge  of 
electricity  thus  urged  toward  the  poles  of  the  earth,  from  whence  it  is 
endeavoring  to  return,  by  natural  and  appointed  means,  above  the 
earth  to  the  equatorial  regions.  The  non-occurrence  of  it  in  very 
high  latitudes  is  not  at  all  against  this  supposition  ; and  it  is  re- 
markable, that  Mr.  Fox,  who  observed  the  deflection  of  the  needle 
at  Falmouth,  gives  that  direction  of  it  which  perfectly  agrees  with 
the  present  view.” 

To  the  new  department  thus  added  by  Mr.  Faraday  to  the 
science  of  Electricity,  he  has  given  the  name  of  Magneto* Elec- 
tricity. 

The  progressive  manner  in  which  he  approached  these  brilliant 
discoveries,  is  worthy  of  attention.  Though  stimulated,  doubtless, 
by  the  hope  of  ultimately  obtaining  electricity  from  ordinary  mag- 
netism, his  first  experiments  were  instituted  simply  with  a design  to 
ascertain  the  inductive  effect  of  electric  currents  ; the  effect,  in  other 
words,  if  any  such  existed,  of  one  current  already  in  motion,  to  excite 
another  in  a neighboring  conductor  of  electricity.  Upon  a wooden 
cylinder,  he  wound  twelve  helices,  containing  on  an  average  twenty- 
seven  feet  of  copper  wire  each,  one  above  another,  and  insulated  by 
calico  interposed.  By  soldering  corresponding  ends  of  the  wires, 
the  first,  third,  fifth,  seventh,  ninth,  and  eleventh  of  these  helices 
were  combined  into  a single  helix  ; and  the  alternate  ones,  in  like 
manner,  into  another.  The  two  compound  helices,  of  about  one 
hundred  and  sixty  feet  each  in  length,  were  thus  interlocked  through- 
out, and  brought  into  close  vicinity  in  every  part  of  their  course. 
Through  one  of  them  Mr.  Faraday  caused  a current  of  electricity 
to  pass,  while  the  extremities  of  the  other  were  connected  with  a 
galvanometer.  The  effect  anticipated  was,  that  the  current  from 
the  battery  circulating  through  one  helix,  would  occasion  another 
current  in  the  other  ; but  no  indication  of  such  an  effect  could  be 
detected.  In  order  to  obtain  a nearer  approach  to  contact,  a new 
double  helix  was  formed,  by  winding  two  hundred  and  three  feet  of 
wire  upon  a wooden  cylinder,  and  the  same  quantity  again  between 
the  coils  of  the  first,  twine  being  interposed  between.  A much 
more  powerful  battery  being  now  used  to  transmit  a current  through 
one  of  the  spirals,  while  the  other  was  connected  with  the  galva- 
nometer, a momentary  and  very  slight  effect  was  perceptible  at  the 
instant  of  either  making  or  breaking  the  connexion  with  the  bat- 


17 


tery ; these  two  effects  being  of  contrary  kinds.  But  during  the 
passage  of  the  battery  current,  however  long  continued  or  intense, 
nothing  like  an  induced  current  could  be  perceived  in  the  other 
wire,  but  the  galvanometer  needle,  from  its  momentary  disturbance 
in  the  beginning,  returned  quietly  to  its  ordinary  position,  where  it 
remained  at  rest  till  the  moment  when  the  voltaic  current  was  sus- 
pended. Then  occurred  the  other  momentary  disturbance,  in  a 
direction  contrary  to  the  former. 

These  momentary  currents  produced  by  induction,  were  in  a di- 
rection contrary  to  that  of  the  inducing  current,  when  the  battery 
contact  was  made ; and  in  the  same  direction,  when  this  contact 
was  broken.  They  were  found  sufficiently  energetic,  when  passed 
through  spiral  conductors,  to  magnetise  steel  needles  ; but  the  suc- 
cessive currents,  being  in  opposite  directions,  produced  in  such 
needles  contrary  polarities.  The  same  needle  being  allowed,  there- 
fore, to  remain  in  the  helix  during  the  first  passage  and  subsequent 
return  of  the  induced  current,  was  found  scarcely  magnetised  at 
all ; but  when  subjected  to  the  single  action  of  either,  exhibited  de- 
cided polarity. 

To  avoid  the  possibility  of  error  from  any  unobserved  peculiarity 
of  circumstances  attendant  upon  making  or  breaking  contact  with 
the  battery,  the  induction  was  then  produced  in  a different  mode. 
Upon  two  separate  boards,  two  similar  zig-zags  of  wire  were  fas- 
tened, so  that  they  could  be  brought  into  mutual  contact  in  every 
part,  except  that  a sheet  of  paper  was  interposed  between.  Being 
separated,  one  of  the  zig-zags  was  connected  with  the  battery,  and 
the  other  with  the  galvanometer.  They  were  then  made  to  approach 
t each  other,  and  at  this  moment  the  galvanometer  indicated  elec- 

tricity. On  being  again  separated,  electricity  of  the  opposite  kind 
was  developed.  With  the  cessation  of  the  motion,  these  currents 
ceased. 

The  fact  of  Yolta-electric  induction  having  been  thus  demon- 
strated in  the  case  of  conductors  contiguous  to  a current  of  elec- 
tricity, Mr.  Faraday  proceeded  to  ascertain  whether  the  same  effect 
would  be  produced  at  a greater  distance,  provided  a communication 
were  formed  by  means  of  iron  rendered  magnetic  by  the  current. 
Two  helices  of  insulated  copper  wire  were  wound  upon  the  opposite 
semicircles  of  an  iron  ring  of  about  six  inches  in  external  diameter. 

3 


18 


An  electric  current  having  been  passed  through  one  of  these,  the 
other  was  traversed  by  momentary  currents,  precisely  as  with  the 
former  arrangement,  but  much  more  powerful.  When  passed 
through  dry  charcoal  points,  they  exhibited  a faint  spark. 

Two  helices  were  then  intertwined  with  each  other  upon  a hol- 
low pasteboard  cylinder,  into  which  was  introduced  a bar  of  iron. 
The  presence  of  the  iron  added  remarkably  to  the  energy  of  the 
induced  currents  : but  this  arrangement  was  inferior  in  power  to 
that  of  the  ring.  A copper  cylinder,  substituted  for  the  iron,  pro- 
duced no  effect ; but  a single  iron  wire  materially  increased  the 
power  of  the  apparatus. 

The  Voltaic  battery  was  then  entirely  disused,  and  the  iron  cy- 
linder in  the  helix,  magnetised,  by  applying  to  its  extremities  the 
contrary  poles  of  two  common  bar  magnets,  each  two  feet  in  length, 
brought  together  at  the  other  extremities,  in  imitation  of  a horse- 
shoe magnet.  Currents  were  still  excited  in  the  helix,  precisely  as 
when  the  battery  was  used.  Their  first  direction,  or  that  which 
occurred  on  making  contact,  was  contrary  to  the  direction  of  the 
currents  supposed,  by  M.  Ampere’s  theory,  to  exist  in  the  magne- 
tised cylinder  ; but  their  returning  direction,  of  course,  corresponded 
with  that  of  these. 

Instead  of  the  soft  iron  cylinder,  a bar,  already  magnetised,  was 
then  employed  alone.  WThen  introduced  into  the  helix,  it  excited 
currents  opposite  to  those  supposed  to  exist  within  itself ; and 
when  withdrawn,  it  produced  others,  corresponding  with  the  same. 
It  was  a matter  of  no  consequence,  as  it  regarded  these  directions, 
at  which  end  of  the  helix  the  magnet  was  first  inserted,  nor,  of 
course,  which  pole  first  entered,  nor  which  way  it  was  moved  ; 
provided  the  same  ends  of  the  magnet  and  helix  continued  to  cor- 
respond in  direction — that  is,  provided  they  were  not  relatively 
reversed. 

Experiments  were  then  made  with  a soft  iron  cylinder,  and  a 
compound  steel  magnet,  of  such  power,  that,  when  the  cylinder  was 
laid  across  the  poles,  nearly  one  hundred  pounds  were  required  to 
break  the  contact.  When  this  cylinder,  surrounded  by  the  helix, 
was  applied  to  the  poles,  the  needle  of  the  galvanometer  was  caused 
to  spin  violently  jound  : but  it  returned  at  length  to  its  quiescent 
state,  if  the  parts  of  the  apparatus  were  kept  motionless,  though 


19 


the  contact  still  continued.  But  when  this  contact  was  broken,  a 
disturbance  quite  as  violent  took  place  in  the  other  direction.  The 
amount  of  effect  produced,  seemed  much  to  depend  upon  the  sudden- 
ness of  making  or  breaking  contact.  When  the  separation  was 
accomplished  by  a blow,  the  currents  were  most  remarkably  de- 
veloped. 

Mr.  Faraday  had  not  yet  obtained  the  electric  spark  from  a 
permanent  steel  magnet  alone,  when  he  announced  his  discoveries, 
in  a private  letter,  to  M.  Hachette  of  Paris.  Imperfect  statements 
of  them  were  soon  made  public ; and  the  experiments  were,  conse- 
quently, at  once  repeated  and  varied  by  numerous  individuals. 
Messrs.  Nobili  and  Antenori  of  Florence,  by  a simple  arrangement, 
elicited  sparks  from  magnets  of  a comparatively  low  power.  A 
coil  of  insulated  wire  was  wound  upon  the  middle  of  the  lifter  (or 
keeper ) of  a horse-shoe  magnet,  the  ends  resting  upon  the  poles  of 
the  horse-shoe  beyond  the  extremities  of  the  lifter,  which  was  made 
short  for  the  purpose.  On  suddenly  breaking  contact  with  the 
poles,  sparks  made  their  appearance  at  the  extremities  of  the  wire. 
Professor  Emmet,  of  Virginia,  has  essentially  improved  this  appa- 
ratus. 

In  March,  1832,  Mr.  J.  D.  Forbes  obtained  the  electric  spark 
from  a natural  magnet,  or  loadstone,  of  great  power  ; the  loadstone 
being  capable  of  sustaining  one  hundred  and  seventy  pounds.  His 
mode  of  exciting  the  currents  was  similar  to  that  of  Faraday,  with 
the  large  compound  steel  magnet  above-mentioned. 

In  October  of  the  same  year,  Mr.  Faraday  contrived  a mode  of 
eliciting  the  spark,  without  the  aid  of  the  soft  iron  cylinder,  or  lifter, 
intervening  between  the  magnet  itself  and  the  conductor  carrying 
the  induced  current,  which  had  hitherto  been  found  necessary  to 
produce  that  phenomenon.  He  fixed  a helix  horizontally  to  a firm 
support,  and  bent  the  two  ends  of  the  wire  to  meet,  one  of  them 
passing  before  the  end  of  the  helix,  or  crossing  the  line  of  its  axis 
continued.  This  end  pressed  with  a spring  against  a little  disk 
soldered  to  the  other.  It  was,  of  course,  impossible  for  a solid  body 
to  pass  through  the  helix  without  striking  the  wire  which  crossed 
its  axis,  and  thus  breaking  the  contact  of  that  wire  with  the  disk. 
If  the  solid  body  were  a magnet,  an  electric  current  would  be  ex- 


20 


cited  in  the  helix  by  its  passage,  and  the  interruption  of  the  contact 
as  above,  would  cause  the  spark  to  appear. 

By  a particular  arrangement,  the  electrical  shock  may  be  obtained 
even  more  directly  from  the  permanent  magnet,  than  the  spark,  as 
just  described.  It  is  known  that  if  a steel  ring  be  magnetised  in 
the  ordinary  way,  by  carrying  round  it  repeatedly  one  of  the  poles 
of  a common  bar-magnet,  it  will,  while  it  remains  whole,  exhibit  no 
polarity.  If,  then,  an  insulated  wire  be  wound  on  a part  of  the 
ring,  and  the  latter  be  suddenly  fractured,  a momentary  current 
will,  at  the  moment  of  the  fracture,  be  induced  in  the  wire,  of  suf- 
ficient intensity  to  produce  a sensible  shock.  This  is  accounted 
for,  by  supposing  that  the  electricity  of  the  magnet  is  obliged  to 
seek  a new  distribution,  when  the  continuity  of  the  ring  is  inter- 
rupted. 

The  first  successful  experiment  of  effecting  chemical  decompo- 
sition by  magneto-electricity,  was  communicated  anonymously  to 
Mr.  Faraday,  in  July,  1832.  It  was  accomplished  by  means  of  an 
ingenious  magneto-electric  machine,  contrived  for  the  double  pur- 
pose of  rendering  available  the  joint  power  of  many  comparatively 
feeble  horse-shoe  magnets,  and  of  increasing  the  facility  of  produc- 
ing the  spark,  by  a sudden  reversal  of  poles.  The  horse-shoe  mag- 
nets were  fixed  equidistant  in  the  circumference  of  a revolving 
wheel,  so  that  their  poles  should  be  even  with  the  surface  of  its 
plane,  and  stand  severally  in  the  lines  of  its  radii.  They  were 
placed  with  their  north  and  south  poles  alternately  outward,  or  at 
the  extreme  edge.  A number  of  lifters  equal  to  that  of  the  mag- 
nets, were  fixed  in  like  manner  in  another  disk  of  wood  of  equal 
size,  placed  motionless,  in  full  contact,  surface  to  surface,  with  the 
wheel.  Thus  all  the  magnets  were,  at  the  same  time,  in  contact 
with  their  respective  lifters.  A single  long  wire  was  wound  round 
the  middle  of  each  lifter,  sucessively,  alternately  from  left  to  right 
and  from  right  to  left,  in  order  that  the  magneto-electric  currents 
excited  by  the  whole  might  be  in  the  same  direction,  though  the 
poles  of  the  magnets  succeeded  each  other  in  contrary  order.  In 
passing  from  lifter  to  lifter,  the  wire  was  wound  round  an  iron  ring 
on  the  outside  of  the  fixed  disk  ; this  being  found  to  increase  the 
power.  Let  us  call  one  of  the  magnets  A,  and  its  next  neighbor 


21 


B.  If,  then,  A has  its  north  pole  outward,  B will  have  its  south 
pole  outward  at  the  same  time.  The  magnet  A produces  a cer- 
tain polarity  in  its  lifters  ; but,  as  the  wheel  turns,  B takes  the  place 
of  A over  the  same  lifter,  and  reverses  that  polarity,  because  its 
poles  stand  in  a contrary  direction.  A similar  change,  from  a simi- 
lar cause,  occurs,  of  course,  throughout  the  whole  apparatus  at 
the  same  moment.  Thus,  if  the  wheel  turns  rapidly,  a rapid  succes- 
sion of  changes  is  constantly  going  on.  If  a little  projection  be 
placed  over  each  magnet,  to  break,  by  a suitable  arrangement,  the 
continuity  of  the  circuit  formed  by  the  wire,  at  the  exact  moment 
of  the  change  of  poles,  the  spark  becomes  visible.  The  currents 
thus  excited  are  found  sufficient  to  decompose  water  ; and  this,  ac- 
cording to  Mr.  Faraday,  was  the  first  arrangement  by  which  that 
object  was  accomplished. 

In  October  of  the  same  year,  Professor  Botto,  of  Turin,  succeeded 
in  effecting  many  decompositions,  and  in  producing  the  spark,  with 
the  aid  of  a magnet  capable  of  lifting  no  more  than  six  pounds. 
Water,  sulphate  of  copper,  and  acetate  of  lead,  were  among  the  sub- 
stances decomposed.  His  magnet  was  placed  in  a box,  with  a soft 
iron  cylinder  wound  with  wire  fixed  before  its  poles.  By  means 
of  a handle,  contact  between  the  poles  and  the  cylinder  could  be 
very  quickly  made  and  broken,  and  a current  of  electricity,  almost 
constant,  kept  up. 

Professor  Dal  Negro,  of  Padua,  contrived,  early  in  1832,  a very 
ingenious  magneto-electrical  battery.  A series  of  parallel  spirals, 
wound  alternately  from  right  to  left  and  from  left  to  right,  and 
formed  all  of  one  wire,  were  placed  opposite  to  the  poles  of  a num- 
ber of  horse-shoe  magnets  fixed  to  a little  carriage,  which  was  so 
constructed,  that,  in  moving,  the  poles  should  be  made  to  pass  se- 
verally within  the  spirals.  All  the  currents  thus  generated  would 
conspire  to  move  in  the  same  general  direction  along  the  wire,  and 
by  the  facility  with  which  the  carriage  could  be  advanced  or  with- 
drawn, they  could  be  kept  up  as  long  as  desired.  ^ 

But  a magneto-electrical  machine,  much  more  efficient  than 
any  that  had  been  previously  constructed,  was  that  invented  in 
1833  by  our  countryman,  Mr.  Joseph  Saxton,  resident  in  London, 
and  denominated  by  him  a revolving-keeper-magnet.  A simple 
drawing  would  serve  to  convey  a better  idea  of  its  construction 


22 


than  many  words.  We  will,  nevertheless,  attempt  a brief  descrip, 
tion.  A horse-shoe  magnet  is  fixed  firmly  in  a horizontal  position. 
Through  the  upper  part,  or  curve,  of  the  horse-shoe,  a horizontal  axis 
passes  longitudinally  to  the  keeper,  which  last  is  wound  with  a 
quantity  of  wire.  Beyond  the  keeper,  on  the  same  axis,  is  a ver- 
tical and  parallel  disk  of  copper,  and  farther  still,  a light  cross- 
bar, all  insulated  from  each  other,  and  the  disk  and  cross-bar  dip- 
ping, as  the  whole  revolves,  into  a basin  of  mercury.  One  end  of 
the  wire  coiled  upon  the  keeper,  touches  the  copper  disk,  and  the 
other  is  carried  along  the  middle  of  the  wooden  axis,  through  the 
centre  of  the  disk,  without  touching,  to  the  cross-bar.  Rapid  rota- 
tion is  then  given  to  the  axis,  carrying  the  keeper,  the  disk,  and 
the  cross-bar,  by  means  of  a wheel  and  band  ; and  as  often  as  the 
point  of  the  cross-bar  leaves  the  surface  of  the  mercury,  a spark  ap- 
pears. By  placing  other  conductors  in  contact  with  the  disk  and 
cross-bar,  the  circuit  may  be  lengthened,  and  made  to  include  an 
apparatus  for  the  purpose  of  effecting  decompositions. 

Soon  after  the  announcement  of  Mr.  Saxton’s  invention,  the  great 
magnet  belonging  to  the  Philadelphia  Museum,  capable  of  sustaining 
a weight  of  134  pounds,  was  fitted  up  into  a magneto-electrical 
machine  by  Mr.  Isaiah  Lukens  of  that  city.  The  “ Journal  of  the 
Franklin  Institute,”  vol.  13,  contains  an  account  of  some  experi- 
ments made  with  that  apparatus,  by  Professor  Green  of  Jefferson 
Medical  College.  Professor  Green  remarks,  that  the  effects  produced 
were  by  no  means  proportional  to  the  power  of  the  magnet ; but  it  is 
probable  that  the  quantity  of  enveloping  wire,  used  to  surround  the 
keeper,  was  altogether  too  small,  since  it  was  not  more  than  one 
third  as  much  in  length  as  is  now  employed  by  Mr.  Saxton,  with 
magnets  of  greatly  inferior  power.  In  his  experiments  on  the 
spark,  Professor  Green  dispensed  with  the  use  of  the  basin  of  mer- 
cury, substituting  strips  of  different  metals,  bent  into  the  form  of 
an  arc,  so  as  to  present  flat  surfaces  to  the  wheel  and  the  cross- 
bar, or  a second  wheel  substituted  in  its  place.  When  a steel  arc 
was  employed,  brilliant  coruscations  and  scintillations  were  pro- 
duced, resembling  those  of  the  same  metal  burning  in  oxygen  gas. 
By  sending  the  current  through  a helix  surrounding  a bar  of  iron, 
electro-magnetic  effects  were  also  produced,  but  less  powerful  than 
had  been  anticipated. 


23 


A contrivance  somewhat  similar  in  principle  to  that  of  Mr.  Sax- 
ton, but  much  simpler  in  construction,  and  less  powerful,  was  in- 
vented by  M.  Pixii,  of  Paris.  In  this,  the  magnet  was  made  to 
rotate,  poles  downward,  over  a fixed  keeper. 

In  the  year  1836,  an  account  was  published  by  Mr.  E.  M.  Clarke 
of  London,  of  a magneto-electrical  machine  constructed  by  him, 
possessing,  as  he  claimed,  important  advantages  over  that  of  Mr. 
Saxton,  and,  indeed,  every  other.  In  principle,  however,  it  seemed 
to  differ  so  little  from  the  contrivance  of  our  ingenious  countryman, 
that  the  latter,  not  without  a show  of  justice,  complained  of  the 
appropriation  of  his  labors.  In  the  apparatus  of  Mr.  Clark,  the  mag- 
net employed  is  fixed  perpendicularly,  poles  downward  ; and  the 
keeper  revolves  against  its  lateral  surface.  The  vessel  of  mercury 
is  inclosed  in  a box,  the  wheel  and  cross-bar  are  dispensed  with, 
and  the  communication  is  made  by  means  of  wires  proceeding  from 
the  box,  and  pressing  on  the  revolving  axis  with  a spring.  In  the 
construction  of  his  later  machines,  Mr.  Clarke  has  dispensed, 
moreover,  entirely  with  the  use  of  the  mercury — a part  of  the  ap- 
paratus which  is  always  troublesome,  and  not  at  all  essential  to  the 
production  of  the  effects. 

Mr.  Clarke  states  that  the  intensity  of  the  magneto-electric 
shock  is  increased  by  employing  a very  long  and  fine  enveloping 
wire  ; but  that  the  spark  is  more  brilliant  when  the  wire  is  of  less 
length  and  greater  diameter.  Few  persons,  he  says,  can  endure 
the  intense  agony  produced  by  his  machine,  when  a small  wire  is 
used,  fifteen  hundred  feet  in  length  : but  the  brightness  of  the  spark 
is  vastly  superior,  when  only  one  hundred  and  twenty  feet  of  a 
coarse  wire  are  substituted  in  its  place. 

In  regard  to  the  magneto-electrical  spark,  Mr.  Faraday  has  made 
a curious  observation ; that  when  a very  long  wire  is  employed, 
the  brilliancy  is  greater  on  breaking  than  on  making  contact, 
while  no  difference  is  perceived  when  the  wire  is  short.  He  con- 
siders this  circumstance  to  be,  not  improbably,  due  to  the  inductive 
action  of  the  current  upon  itself ; that  is,  of  each  portion  of  the 
current  upon  the  rest ; an  action  which,  very  naturally,  takes  place 
when  the  fluid  is  passing  through  the  parallel  coils  of  an  extended 
helix,  and  not  impossibly,  when  the  conductor  is  perfectly  straight. 
The  effect  must,  of  course,  be  proportional  to  the  length  of  the  cir- 


24 


cuit,  and  may  become  imperceptible  when  the  circuit  is  short. 
There  are  many  phenomena  analogous  to  this,  observable  in  elec- 
tricity and  magnetism.  We  know,  for  example,  that  when,  by  ex- 
periment, the  weight  which  a single  pole  of  a magnet  will  sustain 
has  been  determined,  the  application  of  a bar  of  unmagnetized  iron 
to  the  other  pole,  will  so  increase  the  power  of  the  first,  that  a much 
greater  weight  may  be  suspended  from  it  than  before.  This  can  only 
be  accounted  for  by  supposing  that  the  induced  magnetism  of  the  iron 
bar  re-acts,  by  an  opposite  induction,  upon  the  inducing  magnet 
itself,  to  increase  its  magnetic  energy. 

The  magneto- electrical  machines  of  Messrs.  Saxton  and  Clarke, 
operate,  it  will  be  observed,  by  a change  of  polarity  at  every  semi- 
revolution of  the  keeper.  The  direction  of  the  induced  electric 
current  is,  of  course,  reversed  just  as  often.  An  ingenious  con- 
trivance of  Dr.  Ritchie  is  described  in  the  Philosophical  Transac- 
tions for  1833,  for  producing  an  almost  uninterrupted  flow  of  mag- 
neto-electricity in  the  same  direction.  A horse-shoe  magnet  is 
fixed  firmly,  poles  upright,  beneath  a wooden  axis  having  four  arms 
like  those  of  a wind-mill,  the  ends  of  which,  as  the  axis  revolves, 
pass  by  the  poles  of  the  magnet.  To  the  end  of  each  arm  is  fixed 
transversely  a soft  iron  cylinder,  wound  in  the  usual  manner  with 
wire.  The  extremities  of  each  wire  are  carried  along  the  arm,  to 
the  axis,  and  so  to  one  of  the  fixed  supports  in  which  the  axis  turns. 
To  the  inside  and  the  outside  of  this  support  are  fixed  metallic 
disks,  or  portions  of  disks,  the  axis  passing  through  the  centres  of 
both.  Against  the  inside  disk  one  end  of  each  wire  presses,  so  as 
to  remain  in  contact  while  the  revolution  goes  on.  The  other  end 
passes  along  the  interior  of  the  axis  to  the  outside  of  the  support, 
and  is  there  re-curved  so  as  to  press,  in  like  manner,  on  the  outside 
disk.  The  disks  are  connected  severally  with  wires,  which  pass 
off  to  form  a circuit  for  the  ordinary  purposes.  As  the  revolution 
proceeds,  and  each  bar  with  its  coil  approaches  the  magnet,  a flow 
of  electricity  commences  from  it,  which,  as  it  declines  in  one  coil, 
is  renewed  in  that  which  succeeds,  and  so  on  indefinitely. 

We  have  already  observed  that  a flow  of  electricity,  perfectly 
continuous,  is  excited  by  the  magnetic  action  of  the  earth  upon  a 
circular  metallic  plate,  revolving  at  right  angles  to  the  line  of  the 
dip.  Mr.  Faraday,  in  1832,  suggested  the  construction  of  a mag- 


25 


neto-electrical  machine  of  considerable  power,  on  this  simple  prin- 
ciple alone.  When  the  rotation  of  the  plate  is  made  to  correspond 
in  direction  with  that  of  the  earth,  that  is  from  west  to  east,  the 
electrical  currents  excited,  tend  toward  the  axis,  from  the  circum- 
ference ; and  the  reverse,  when  the  direction  of  rotation  is  reversed. 
Mr.  Faraday  would,  accordingly,  have  had  a number  of  parallel 
disks  to  revolve  about  a common  axis  of  motion,  and  in  contact 
with  one  another  only  at  the  centres  and  circumferences  alternately, 
the  alternate  disks  revolving  in  contrary  directions.  The  effect  of 
such  an  arrangement  will  be  obvious  to  a little  thought.  If  we 
suppose  the  currents  to  be  proceeding  outward,  on  the  surface  of 
the  first  disk,  they  will,  on  arriving  at  the  circumference,  pass  to 
the  next  disk,  where  the  currents  are  at  the  same  time  flowing  in- 
ward ; making  the  volume  of  those  inward  currents  two-fold.  On 
reaching  the  centre,  they  will  pass  to  the  third  disk,  and  flow  outward 
again,  with  a volume  a second  time  augmented.  The  electricity 
will  thus  continue  to  accumulate  to  the  end  of  the  series. 

We  are  not  aware  that  any  machine  has  ever  been  actually  con- 
structed on  this  principle.  In  making  the  suggestion,  Mr,  Faraday 
remarks,  as  a reason  for  not  having  carried  it  out  in  practice,  that  he 
has  chosen  rather  to  busy  himself  in  seeking  for  new  modes  of 
evolving  this  mysterious  agent,  than  in  endeavoring,  by  improved 
mechanical  arrangements,  which  must  follow  of  course  in  due  time, 
to  render  more  striking  the  effects  of  those  already  known.  Such 
seems  to  have  been  the  spirit  by  which  all  the  great  discoverers  in 
this  novel  and  brilliant  department  of  natural  science  have  been 
actuated.  New  and  beautiful  facts  have  been  coming  to  light  in  so 
rapid  succession,  within  the  past  ten  years,  that  every  philosophic 
investigator  has  felt  himself  excited  to  emulation  by  the  hope  of 
being  first  to  announce  to  the  world  each  additional  extraordinary 
discovery  ; and  of  thus  more  surely  linking  his  name  forever  to 
the  history  of  the  science.  This  may,  in  part,  account  for  the 
comparatively  little  attention  which  the  philosophers  have  given  to 
the  subject  of  employing  electro-magnetism  as  a moving  power. 
Motion,  they  have  from  time  to  time  produced,  with  feeble  apparatus  ; 
but  they  have,  in  very  few  instances,  applied  themselves  to  the  task 
of  testing,  in  practice,  how  great  might  be  the  possible  energy  of 
more  perfect  arrangements.  Dr.  Ritchie,  it  is  true,  in  some  of  his 
4 


26 


later  publications,  has  pronounced  his  rotating  invention  to  be 
practically  useless  ; assigning  its  inutility  as  a reason  for  having 
laid  it  aside  : but  he  has  never  devoted  that  patient  industry  to  its 
improvement,  which  he  has  been  ever  ready  to  contribute  to  the 
advancement  of  science.  Mr.  Sturgeon  also  laid  aside  his  ma- 
chine, but  only  because  he  thought  it  might  be  improved  ; yet  no 
gentleman  has  been  more  indefatigable  than  he  in  the  field  of  phi- 
losophical inquiry. 

Having  proposed  to  ourselves  merely  a popular  sketch  of  this 
interesting  science,  we  must  here  draw  our  remarks  to  a close.  It 
is  proper  to  observe,  however,  that  the  question,  long  esteemed 
doubtful,  whether  electricity,  under  all  the  various  forms  in  which 
it  manifests  itself  to  us,  or  by  whatever  mode  excited  from  its  latent 
state,  is  in  fact,  or  not,  always  identically  the  same,  is  admitted  to 
have  been  set  at  rest  by  the  masterly  investigations  of  Mr.  Faraday. 
The  various  forms  alluded  to,  are  Volta-Electricity,  Magneto-Elec- 
tricity, Thermo-Electricity,  Animal  Electricity,  and  common  Elec- 
tricity of  tension.  Since  Mr.  Faraday’s  experiments  on  this  subject, 
the  march  of  ^science  has  furnished  additional  corroborations  of  his 
conclusions.  Among  these  may  be  mentioned  the  production  of  the 
electric  spark  from  the  torpedo,  and  from  thermo-electrical  apparatus. 

It  would  be  aside  from  our  purpose,  however,  to  follow  out  in 
detail  the  interesting  discoveries  made,  in  late  years,  in  any  other 
department  of  electrical  science,  than  that  to  which  we  have  given 
particular  consideration  in  this  cursory  view.  That  alone  is  full  of 
wonders  ; and  of  these,  if  we  have  succeeded  in  imperfectly  describ- 
ing some  of  the  most  remarkable,  our  object  is  accomplished. 


NOTE. 

Since  the  commencement  of  the  present  sketch  was  put  in  type 
as  an  article  in  the  American  Monthly  Magazine,  the  October 
number  of  Professor  Silliman’s  Journal  of  Science  has  made  its 
appearance,  containing  an  account  of  an  Electro-Magnetic  machine, 
constructed  by  Dr.  Benjamin  Rush  McConnell,  of  Mauch  Chunk, 
Pennsylvania.  This  machine  is,  in  principle,  entirely  different 
from  any  previous  contrivance  of  the  kind  ; and  yet  it  can  hardly 
be  called  a new  invention,  since  it  is  only  a copy,  on  a large  scale, 
of  an  electro-magnetic  trifle  long  known  to  experimenters.  That 
it  may  be  understood,  it  will  be  necessary  to  recal  the  phenomena 


27 


of  the  rotation  of  conductors  around  magnetic  poles,  mentioned  in 
the  beginning  of  this  outline.  Suppose  a magnet  to  be  fixed  in  a 
basin  of  mercury,  the  south  pole  upward,  and  a jointed  wire  to  con- 
vey a current  of  electricity  downward  to  the  mercury.  The  wire 
will  immediate^  commence  a rotation  in  what  is  called  the  unscrew 
direction  : that  is,  from  right  to  left.  If  a north  pole  be  employed, 
the  rotation  will  take  place  in  the  opposite,  or  screw  direction  ; that 
is,  from  left  to  right.  If  then,  a horse-shoe  magnet,  with  both  poles 
upward,  be  employed,  the  wire  descending  between  the  poles  will, 
in  the  first  instant,  be  impelled  by  both  in  the  same  direction  ; but, 
immediately  afterward,  will  be  urged  by  one  to  deviate  to  the  right, 
and  by  the  other,  to  the  left ; so  that,  between  the  two,  it  will  pro. 
ceed  in  a straight  line  till  it  is  carried  out  of  the  mercury.  If  the 
wire  be  replaced  by  a wheel,  the  edge  just  touching  the  mercury,  it 
is  obvious  that  the  wheel  will  revolve,  so  long  as  the  current  con- 
tinues. A current  going  upward  from  the  mercury,  the  position  of 
the  magnet  remaining  the  same,  will  reverse  the  motion  of  the 
wheel.  This  motion  may  also  be  reversed  by  causing  the  poles  of 
the  magnet  to  exchange  places.  The  little  apparatus  alluded  to 
above,  consists  of  two  disks,  turning  in  separate  channels  of  mercury, 
and  attached  to  the  ends  of  a common  metallic  axis.  The  channels 
of  mercury  severally  communicate  witn  the  opposite  ends  of  a vol- 
taic battery.  Thus  a current  of  electricity  passes  upward  in  one 
wheel,  then  along  the  axis,  and  finally  downward  in  4he  other.  Two 
horse-shoe  magnets  are  laid,  one  to  embrace  each  ^eel,  in  such  a 
manner  that  they  may  act  unitedly  to  produce  rotati^l  in  the  same 
direction.  ^ 

This  piece  of  apparatus  is  the  model  of  Mr.  McConnell’s  ma- 
chine. He  takes  advantage  of  no  change  of  poles,  but  derives  his 
available  force  wholly  from  an  enlargement  of  the  disks,  and  an  in- 
crease in  the  energy  of  the  magnets  (electro-magnets)  employed. 
He  dispenses,  also,  with  the  use  of  the  mercury.  He  employs  hollow 
electro-magnets,  and  says  he  has  succeeded  equally  well  with  them, 
whether  made  of  bar  iron,  tinned  iron,  or  copper.  Their  diameter 
is  one  inch  ; their  length  five  and  a half  inches  ; distance  between 
the  poles,  one  and  a half  inches ; quantity  of  wire  (iron  wire) 
surrounding  each,  one  hundred  and  fifty  feet.  His  battery  is  an 
external  copper  cube  of  seven  inches  ; the  zinc,  six  and  a half 
inches  edge,  by  seven  deep,  with  another  interior  copper  surface ; 
entire  galvanic  surface  of  zinc,  about  two  square  feet.  The 
copper  disks  are  nine  inches  each  in  diameter  ; and,  on  the  middle 
of  the  axis,  is  a band-wheel  to  communicate  motion  to  machinery, 
sixteen  inches  in  diameter.  The  shaft  is  of  iron,  three-eighths  of  an 
inch  in  diameter,  by  five  inches  long.  The  machine  moves  a car- 
riage on  which  it  is  fixed.  When  not  attached  to  its  load,  it  makes 
two  hundred  revolutions  per  minute.  Loaded  with  forty  pounds,  it 
revolves  seventy  times  per  minute,  and  moves  over  a space  of  two 
hundred  and  eighty  feet  in  the  same  time.  It  has  been  in  opera- 
tion more  than  a year.  Dr.  McConnell  has  not  constructed  any 
other  similar  machine  on  a larger  scale  ; his  professional  duties  in- 
terfering, as  he  says,  with  the  prosecution  of  his  experiments. 


28 


3 0112  072884932 


We  have  been  more  particular  in  the  description  of  this  machine, 
because  its  performances,  as  stated,  astonish  us,  when  we  consider 
that  the  power  employed  is  only  that  of  a single  current  of  electri- 
city, re-acting,  by  its  tangential  force,  upon  the  poles  of  magnets ; 
the  parts  of  the  apparatus  not  being,  either,  in  very  close  juxtapo- 
sition. It  is  to  be  desired  that  a careful  series  of  experiments 
should  be  instituted,  to  ascertain  how  far  this  principle  may  be  use- 
ful. 

Electro-magnetic  machines  are  coming  into  existence  every- 
where. We  hear  that  Professor  Dal  Negro,  of  Padua,  has  produc- 
ed an  invention  of  the  kind ; and  that  the  same  power  has  been  suc- 
cessfully applied  so  far  off  as  Calcutta.  It  is  more  than  eighteen 
months  since  we  heard  of  a magnetic  loco-motive,  set  in  operation 
by  M.  Lemaire  of  Brussels.  M.  Lemaire  was  probably  less  suc- 
cessful than  he  had  hoped  to  be,  for  he  has  been  already  forgotten. 
The  Emperor  of  Russia  is  said  to  have  directed  a grand  series  of 
experiments  to  be  instituted,  for  the  sake  of  settling  the  question 
how  far  electro-magnetism  can  be  employed  as  a moving  power. 
Our  countrymen,  Messrs.  Davenport  and  Cooke,  are  preparing  to 
set  in  operation  a Napier  press,  with  a working  wheel  of  thirty 
inches  diameter,  and  two  oriiree  horse  power. 

In  the  mean  time,  there  ajre  not  wanting  sceptics,  who  expect  to 
see  these  laudable  enterprises  abandoned  for  want  of  success. 
They  expect,  ail  most,  onljf  that  electro-magnetism  will  be  applied 
to  those  opera^&ns  in  the  arts  which  require  but  a trifling  motive 
power  ; whiljReam  is,  in  their  opinion,  destined  for  ever  to  perform, 
without  a ri/*al,  those  gigantic  labors,  which  have  already  wrought 
so  complete  a social,  mechanical,  and  commercial  revolution 
throughout  the  civilized  world.  No  great  improvement  in  science 
or  the  arts  wras  ever  yet  received  with  hearty  welcome  or  regarded 
with  undoubting  confidence  in  the  outset,  by  those  whom  it  was 
destined  to  benefit.  Such  things  must  f rce  their  own  way  to  cele- 
brity. Prejudice  must  be  demolished,  distrust  overthrown,  ridi- 
cule rendered  ridiculous,  and  opposition  cc^ifounded,  by  the  straight- 
forward logic  of  facts.  Let  the  humble  but  sagacious  experimen- 
ter, in  the  solitude  of  his  laboratory,  estimate  at  what  it  is  worth, 
the  profundity  that  would  demonstrate  iq  advance  the  folly  of  his 
undertaking,  or  the  shallowness  that  would  pretend  to  pity  or  des- 
pise, because  incapable  of  comprehending  ; he  knows  that  in  the 
hour  in  which  he  shall  announce  his  triumph,  the  reasoners  and 
the  sneerers  will  alike  be  put  to  silence,  by  an  argument  to  which  they 
must,  as  it  is  the  only  argument  to  which  tihey  ever  will,  submit.  It 
is  a very  just  remark  of  a German  writer,  that,  “ though  it  requires 
but  little  wit  to  be  of  an  opinion  now,  which  all  the  world  arrived 
at  twenty  years  ago ; it  bespeaks  no  slight  superiority  of  mind  to 
entertain  already  an  opinion,  in  which  all  the  world  will  not  be 
prepared  to  concur  for  twenty  years  to  come.” 


